1. Technical Field
The present invention relates to an appartus and method for protecting commercial airliners from man portable missiles.
2. Background Art
There is a growing concern that terrorists will use shoulder-fired, heat-seeking missiles to shoot down commercial airliners. Many portable heat-seeking missiles are inexpensive, relatively easy to obtain on the black market and extremely dangerous. Afghan rebels used U.S.-supplied Stinger missiles to destroy Soviet jets and attack helicopters in the 1980s. Terrorists have recently tried to use older, Soviet-made SA-7 shoulder-fired missiles to bring down U.S. military aircraft in Saudi Arabia and an Israeli airliner in Kenya.
Neighborhoods or other areas where terrorists could hide and attack commercial jet airliners as they land or take off surround many of the world""s civilian airports. Jets that routinely cruise at 500 mph or faster fly much more slowly near the ground. A Boeing 737 typically flies both take-off climb-out and landing approaches at 150-160 mph, for example. Even slow shoulder-fired missiles can fly almost 1,000 mph, more than fast enough to overtake a jet.
A heat-seeking missile operates much like a point-and-shoot camera. The operator aims at one of a plane""s engines, which are heat sources, xe2x80x9clocks onxe2x80x9d the target for about six seconds, and fires. The missile has an infrared sensor that xe2x80x9cseesxe2x80x9d the aircraft""s heat plume; a computer navigational system guides the weapon to an engine. A commercial pilot would almost never see a missile coming and could generally react only after the missile hit an engine or exploded nearby.
Certain US Air Force aircraft, such as C-17 cargo jets, have equipment to thwart attacks from portable heat-seeking missiles. It is known in the art to protect such aircraft by providing, on the aircraft, missile-detecting sensors coupled to a processor, which determines whether a missile is present, and flare and or chaff dispensers that explode flares or chaff to divert the missile away from the aircraft. However, the cost to install and maintain such equipment on many civilian aircraft would be very expensive, the missile detection algorithms are military sensitive knowledge, and it would be both unwise and unacceptable to install a pyrotechnic on a civilian aircraft.
There are roughly 5,000 commercial aircraft owned by U.S. carriers and 10,000 more in the rest of the world. There is a need to protect these commercial airliners from man portable missiles.
In accordance with my invention, a missile sensor head is mounted on an airliner and transmits raw sensor video to a series of ground stations. The carrier frequency for this transmission provides a very precise timing signal that allows the ground stations to track the aircraft to centimeter position accuracy.
The ground stations track the aircraft""s position and process the raw sensor video. A gun turret adapted for accurately placing and detonating flare cartridges is positioned on the ground adjacent to the runway and tracks the aircraft as it flies through a protected zone. When the ground station determines that a missile is being viewed by the airliner-mounted missile sensor head, the gun turret lays down a predetermined pattern of exploding flares to divert the missile away from the airliner.
In a further embodiment of my invention, each airliner is equipped with multiple aircraft sensor packages and each aircraft sensor package transmits on a unique carrier frequency allowing the ground stations to determine both precise airliner position and pitch, roll and heading attitude. These aircraft sensor packages are remotely controlled by air traffic control and only transmit while the airliner is in a protected area. In a preferred embodiment of my invention, the carrier frequency is also remotely selected by air traffic control and is within the already allocated radio navigation frequency band of 108.000 to 117.975 MHz.
Precise aircraft location is obtained by tracking the carrier phase of a transmitted signal in a manner similar to that used for global positioning system (GPS) carrier phase tracking. In the present invention, three receivers are phase tracking a single transmitter whereas in GPS surveying, a single receiver tracks three transmitters. Kinematic phase tracking requires that the receivers xe2x80x98lock onxe2x80x99 to the transmitted signal and continuously monitor phase shift and full-wave cycle count.
Using a radio frequency (RF) signal to measure a physical distance, where that distance is less than less the wavelength of the RF signal by measuring phase shift using of a transmitted signal against a reference oscillator is very well known. Kinematic phase tracking is a technique that not only measures the fractional part, relative to reference RF signal, of a distance, but also xe2x80x98countsxe2x80x99 the number of complete RF cycles by constantly monitoring the changing phase shift of RF signal and whether the distance is increasing or decreasing. Kinematic phase tracking requires that each ground station count the whole and partial RF cycles, where each RF cycle corresponds to a wavelength, starting from a known distance. In my invention this known distance for each ground station corresponds to the distance between the aircraft sensor package and each ground station while the aircraft is located at a xe2x80x98survey positionxe2x80x99.